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Linux/mm/mremap.c

  1 /*
  2  *      mm/mremap.c
  3  *
  4  *      (C) Copyright 1996 Linus Torvalds
  5  *
  6  *      Address space accounting code   <alan@lxorguk.ukuu.org.uk>
  7  *      (C) Copyright 2002 Red Hat Inc, All Rights Reserved
  8  */
  9 
 10 #include <linux/mm.h>
 11 #include <linux/hugetlb.h>
 12 #include <linux/shm.h>
 13 #include <linux/ksm.h>
 14 #include <linux/mman.h>
 15 #include <linux/swap.h>
 16 #include <linux/capability.h>
 17 #include <linux/fs.h>
 18 #include <linux/swapops.h>
 19 #include <linux/highmem.h>
 20 #include <linux/security.h>
 21 #include <linux/syscalls.h>
 22 #include <linux/mmu_notifier.h>
 23 #include <linux/sched/sysctl.h>
 24 
 25 #include <asm/uaccess.h>
 26 #include <asm/cacheflush.h>
 27 #include <asm/tlbflush.h>
 28 
 29 #include "internal.h"
 30 
 31 static pmd_t *get_old_pmd(struct mm_struct *mm, unsigned long addr)
 32 {
 33         pgd_t *pgd;
 34         pud_t *pud;
 35         pmd_t *pmd;
 36 
 37         pgd = pgd_offset(mm, addr);
 38         if (pgd_none_or_clear_bad(pgd))
 39                 return NULL;
 40 
 41         pud = pud_offset(pgd, addr);
 42         if (pud_none_or_clear_bad(pud))
 43                 return NULL;
 44 
 45         pmd = pmd_offset(pud, addr);
 46         if (pmd_none(*pmd))
 47                 return NULL;
 48 
 49         return pmd;
 50 }
 51 
 52 static pmd_t *alloc_new_pmd(struct mm_struct *mm, struct vm_area_struct *vma,
 53                             unsigned long addr)
 54 {
 55         pgd_t *pgd;
 56         pud_t *pud;
 57         pmd_t *pmd;
 58 
 59         pgd = pgd_offset(mm, addr);
 60         pud = pud_alloc(mm, pgd, addr);
 61         if (!pud)
 62                 return NULL;
 63 
 64         pmd = pmd_alloc(mm, pud, addr);
 65         if (!pmd)
 66                 return NULL;
 67 
 68         VM_BUG_ON(pmd_trans_huge(*pmd));
 69 
 70         return pmd;
 71 }
 72 
 73 static pte_t move_soft_dirty_pte(pte_t pte)
 74 {
 75         /*
 76          * Set soft dirty bit so we can notice
 77          * in userspace the ptes were moved.
 78          */
 79 #ifdef CONFIG_MEM_SOFT_DIRTY
 80         if (pte_present(pte))
 81                 pte = pte_mksoft_dirty(pte);
 82         else if (is_swap_pte(pte))
 83                 pte = pte_swp_mksoft_dirty(pte);
 84         else if (pte_file(pte))
 85                 pte = pte_file_mksoft_dirty(pte);
 86 #endif
 87         return pte;
 88 }
 89 
 90 static void move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd,
 91                 unsigned long old_addr, unsigned long old_end,
 92                 struct vm_area_struct *new_vma, pmd_t *new_pmd,
 93                 unsigned long new_addr, bool need_rmap_locks)
 94 {
 95         struct address_space *mapping = NULL;
 96         struct anon_vma *anon_vma = NULL;
 97         struct mm_struct *mm = vma->vm_mm;
 98         pte_t *old_pte, *new_pte, pte;
 99         spinlock_t *old_ptl, *new_ptl;
100 
101         /*
102          * When need_rmap_locks is true, we take the i_mmap_mutex and anon_vma
103          * locks to ensure that rmap will always observe either the old or the
104          * new ptes. This is the easiest way to avoid races with
105          * truncate_pagecache(), page migration, etc...
106          *
107          * When need_rmap_locks is false, we use other ways to avoid
108          * such races:
109          *
110          * - During exec() shift_arg_pages(), we use a specially tagged vma
111          *   which rmap call sites look for using is_vma_temporary_stack().
112          *
113          * - During mremap(), new_vma is often known to be placed after vma
114          *   in rmap traversal order. This ensures rmap will always observe
115          *   either the old pte, or the new pte, or both (the page table locks
116          *   serialize access to individual ptes, but only rmap traversal
117          *   order guarantees that we won't miss both the old and new ptes).
118          */
119         if (need_rmap_locks) {
120                 if (vma->vm_file) {
121                         mapping = vma->vm_file->f_mapping;
122                         mutex_lock(&mapping->i_mmap_mutex);
123                 }
124                 if (vma->anon_vma) {
125                         anon_vma = vma->anon_vma;
126                         anon_vma_lock_write(anon_vma);
127                 }
128         }
129 
130         /*
131          * We don't have to worry about the ordering of src and dst
132          * pte locks because exclusive mmap_sem prevents deadlock.
133          */
134         old_pte = pte_offset_map_lock(mm, old_pmd, old_addr, &old_ptl);
135         new_pte = pte_offset_map(new_pmd, new_addr);
136         new_ptl = pte_lockptr(mm, new_pmd);
137         if (new_ptl != old_ptl)
138                 spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING);
139         arch_enter_lazy_mmu_mode();
140 
141         for (; old_addr < old_end; old_pte++, old_addr += PAGE_SIZE,
142                                    new_pte++, new_addr += PAGE_SIZE) {
143                 if (pte_none(*old_pte))
144                         continue;
145                 pte = ptep_get_and_clear(mm, old_addr, old_pte);
146                 pte = move_pte(pte, new_vma->vm_page_prot, old_addr, new_addr);
147                 pte = move_soft_dirty_pte(pte);
148                 set_pte_at(mm, new_addr, new_pte, pte);
149         }
150 
151         arch_leave_lazy_mmu_mode();
152         if (new_ptl != old_ptl)
153                 spin_unlock(new_ptl);
154         pte_unmap(new_pte - 1);
155         pte_unmap_unlock(old_pte - 1, old_ptl);
156         if (anon_vma)
157                 anon_vma_unlock_write(anon_vma);
158         if (mapping)
159                 mutex_unlock(&mapping->i_mmap_mutex);
160 }
161 
162 #define LATENCY_LIMIT   (64 * PAGE_SIZE)
163 
164 unsigned long move_page_tables(struct vm_area_struct *vma,
165                 unsigned long old_addr, struct vm_area_struct *new_vma,
166                 unsigned long new_addr, unsigned long len,
167                 bool need_rmap_locks)
168 {
169         unsigned long extent, next, old_end;
170         pmd_t *old_pmd, *new_pmd;
171         bool need_flush = false;
172         unsigned long mmun_start;       /* For mmu_notifiers */
173         unsigned long mmun_end;         /* For mmu_notifiers */
174 
175         old_end = old_addr + len;
176         flush_cache_range(vma, old_addr, old_end);
177 
178         mmun_start = old_addr;
179         mmun_end   = old_end;
180         mmu_notifier_invalidate_range_start(vma->vm_mm, mmun_start, mmun_end);
181 
182         for (; old_addr < old_end; old_addr += extent, new_addr += extent) {
183                 cond_resched();
184                 next = (old_addr + PMD_SIZE) & PMD_MASK;
185                 /* even if next overflowed, extent below will be ok */
186                 extent = next - old_addr;
187                 if (extent > old_end - old_addr)
188                         extent = old_end - old_addr;
189                 old_pmd = get_old_pmd(vma->vm_mm, old_addr);
190                 if (!old_pmd)
191                         continue;
192                 new_pmd = alloc_new_pmd(vma->vm_mm, vma, new_addr);
193                 if (!new_pmd)
194                         break;
195                 if (pmd_trans_huge(*old_pmd)) {
196                         int err = 0;
197                         if (extent == HPAGE_PMD_SIZE) {
198                                 VM_BUG_ON(vma->vm_file || !vma->anon_vma);
199                                 /* See comment in move_ptes() */
200                                 if (need_rmap_locks)
201                                         anon_vma_lock_write(vma->anon_vma);
202                                 err = move_huge_pmd(vma, new_vma, old_addr,
203                                                     new_addr, old_end,
204                                                     old_pmd, new_pmd);
205                                 if (need_rmap_locks)
206                                         anon_vma_unlock_write(vma->anon_vma);
207                         }
208                         if (err > 0) {
209                                 need_flush = true;
210                                 continue;
211                         } else if (!err) {
212                                 split_huge_page_pmd(vma, old_addr, old_pmd);
213                         }
214                         VM_BUG_ON(pmd_trans_huge(*old_pmd));
215                 }
216                 if (pmd_none(*new_pmd) && __pte_alloc(new_vma->vm_mm, new_vma,
217                                                       new_pmd, new_addr))
218                         break;
219                 next = (new_addr + PMD_SIZE) & PMD_MASK;
220                 if (extent > next - new_addr)
221                         extent = next - new_addr;
222                 if (extent > LATENCY_LIMIT)
223                         extent = LATENCY_LIMIT;
224                 move_ptes(vma, old_pmd, old_addr, old_addr + extent,
225                           new_vma, new_pmd, new_addr, need_rmap_locks);
226                 need_flush = true;
227         }
228         if (likely(need_flush))
229                 flush_tlb_range(vma, old_end-len, old_addr);
230 
231         mmu_notifier_invalidate_range_end(vma->vm_mm, mmun_start, mmun_end);
232 
233         return len + old_addr - old_end;        /* how much done */
234 }
235 
236 static unsigned long move_vma(struct vm_area_struct *vma,
237                 unsigned long old_addr, unsigned long old_len,
238                 unsigned long new_len, unsigned long new_addr, bool *locked)
239 {
240         struct mm_struct *mm = vma->vm_mm;
241         struct vm_area_struct *new_vma;
242         unsigned long vm_flags = vma->vm_flags;
243         unsigned long new_pgoff;
244         unsigned long moved_len;
245         unsigned long excess = 0;
246         unsigned long hiwater_vm;
247         int split = 0;
248         int err;
249         bool need_rmap_locks;
250 
251         /*
252          * We'd prefer to avoid failure later on in do_munmap:
253          * which may split one vma into three before unmapping.
254          */
255         if (mm->map_count >= sysctl_max_map_count - 3)
256                 return -ENOMEM;
257 
258         /*
259          * Advise KSM to break any KSM pages in the area to be moved:
260          * it would be confusing if they were to turn up at the new
261          * location, where they happen to coincide with different KSM
262          * pages recently unmapped.  But leave vma->vm_flags as it was,
263          * so KSM can come around to merge on vma and new_vma afterwards.
264          */
265         err = ksm_madvise(vma, old_addr, old_addr + old_len,
266                                                 MADV_UNMERGEABLE, &vm_flags);
267         if (err)
268                 return err;
269 
270         new_pgoff = vma->vm_pgoff + ((old_addr - vma->vm_start) >> PAGE_SHIFT);
271         new_vma = copy_vma(&vma, new_addr, new_len, new_pgoff,
272                            &need_rmap_locks);
273         if (!new_vma)
274                 return -ENOMEM;
275 
276         moved_len = move_page_tables(vma, old_addr, new_vma, new_addr, old_len,
277                                      need_rmap_locks);
278         if (moved_len < old_len) {
279                 /*
280                  * On error, move entries back from new area to old,
281                  * which will succeed since page tables still there,
282                  * and then proceed to unmap new area instead of old.
283                  */
284                 move_page_tables(new_vma, new_addr, vma, old_addr, moved_len,
285                                  true);
286                 vma = new_vma;
287                 old_len = new_len;
288                 old_addr = new_addr;
289                 new_addr = -ENOMEM;
290         }
291 
292         /* Conceal VM_ACCOUNT so old reservation is not undone */
293         if (vm_flags & VM_ACCOUNT) {
294                 vma->vm_flags &= ~VM_ACCOUNT;
295                 excess = vma->vm_end - vma->vm_start - old_len;
296                 if (old_addr > vma->vm_start &&
297                     old_addr + old_len < vma->vm_end)
298                         split = 1;
299         }
300 
301         /*
302          * If we failed to move page tables we still do total_vm increment
303          * since do_munmap() will decrement it by old_len == new_len.
304          *
305          * Since total_vm is about to be raised artificially high for a
306          * moment, we need to restore high watermark afterwards: if stats
307          * are taken meanwhile, total_vm and hiwater_vm appear too high.
308          * If this were a serious issue, we'd add a flag to do_munmap().
309          */
310         hiwater_vm = mm->hiwater_vm;
311         vm_stat_account(mm, vma->vm_flags, vma->vm_file, new_len>>PAGE_SHIFT);
312 
313         if (do_munmap(mm, old_addr, old_len) < 0) {
314                 /* OOM: unable to split vma, just get accounts right */
315                 vm_unacct_memory(excess >> PAGE_SHIFT);
316                 excess = 0;
317         }
318         mm->hiwater_vm = hiwater_vm;
319 
320         /* Restore VM_ACCOUNT if one or two pieces of vma left */
321         if (excess) {
322                 vma->vm_flags |= VM_ACCOUNT;
323                 if (split)
324                         vma->vm_next->vm_flags |= VM_ACCOUNT;
325         }
326 
327         if (vm_flags & VM_LOCKED) {
328                 mm->locked_vm += new_len >> PAGE_SHIFT;
329                 *locked = true;
330         }
331 
332         return new_addr;
333 }
334 
335 static struct vm_area_struct *vma_to_resize(unsigned long addr,
336         unsigned long old_len, unsigned long new_len, unsigned long *p)
337 {
338         struct mm_struct *mm = current->mm;
339         struct vm_area_struct *vma = find_vma(mm, addr);
340 
341         if (!vma || vma->vm_start > addr)
342                 goto Efault;
343 
344         if (is_vm_hugetlb_page(vma))
345                 goto Einval;
346 
347         /* We can't remap across vm area boundaries */
348         if (old_len > vma->vm_end - addr)
349                 goto Efault;
350 
351         /* Need to be careful about a growing mapping */
352         if (new_len > old_len) {
353                 unsigned long pgoff;
354 
355                 if (vma->vm_flags & (VM_DONTEXPAND | VM_PFNMAP))
356                         goto Efault;
357                 pgoff = (addr - vma->vm_start) >> PAGE_SHIFT;
358                 pgoff += vma->vm_pgoff;
359                 if (pgoff + (new_len >> PAGE_SHIFT) < pgoff)
360                         goto Einval;
361         }
362 
363         if (vma->vm_flags & VM_LOCKED) {
364                 unsigned long locked, lock_limit;
365                 locked = mm->locked_vm << PAGE_SHIFT;
366                 lock_limit = rlimit(RLIMIT_MEMLOCK);
367                 locked += new_len - old_len;
368                 if (locked > lock_limit && !capable(CAP_IPC_LOCK))
369                         goto Eagain;
370         }
371 
372         if (!may_expand_vm(mm, (new_len - old_len) >> PAGE_SHIFT))
373                 goto Enomem;
374 
375         if (vma->vm_flags & VM_ACCOUNT) {
376                 unsigned long charged = (new_len - old_len) >> PAGE_SHIFT;
377                 if (security_vm_enough_memory_mm(mm, charged))
378                         goto Efault;
379                 *p = charged;
380         }
381 
382         return vma;
383 
384 Efault: /* very odd choice for most of the cases, but... */
385         return ERR_PTR(-EFAULT);
386 Einval:
387         return ERR_PTR(-EINVAL);
388 Enomem:
389         return ERR_PTR(-ENOMEM);
390 Eagain:
391         return ERR_PTR(-EAGAIN);
392 }
393 
394 static unsigned long mremap_to(unsigned long addr, unsigned long old_len,
395                 unsigned long new_addr, unsigned long new_len, bool *locked)
396 {
397         struct mm_struct *mm = current->mm;
398         struct vm_area_struct *vma;
399         unsigned long ret = -EINVAL;
400         unsigned long charged = 0;
401         unsigned long map_flags;
402 
403         if (new_addr & ~PAGE_MASK)
404                 goto out;
405 
406         if (new_len > TASK_SIZE || new_addr > TASK_SIZE - new_len)
407                 goto out;
408 
409         /* Check if the location we're moving into overlaps the
410          * old location at all, and fail if it does.
411          */
412         if ((new_addr <= addr) && (new_addr+new_len) > addr)
413                 goto out;
414 
415         if ((addr <= new_addr) && (addr+old_len) > new_addr)
416                 goto out;
417 
418         ret = do_munmap(mm, new_addr, new_len);
419         if (ret)
420                 goto out;
421 
422         if (old_len >= new_len) {
423                 ret = do_munmap(mm, addr+new_len, old_len - new_len);
424                 if (ret && old_len != new_len)
425                         goto out;
426                 old_len = new_len;
427         }
428 
429         vma = vma_to_resize(addr, old_len, new_len, &charged);
430         if (IS_ERR(vma)) {
431                 ret = PTR_ERR(vma);
432                 goto out;
433         }
434 
435         map_flags = MAP_FIXED;
436         if (vma->vm_flags & VM_MAYSHARE)
437                 map_flags |= MAP_SHARED;
438 
439         ret = get_unmapped_area(vma->vm_file, new_addr, new_len, vma->vm_pgoff +
440                                 ((addr - vma->vm_start) >> PAGE_SHIFT),
441                                 map_flags);
442         if (ret & ~PAGE_MASK)
443                 goto out1;
444 
445         ret = move_vma(vma, addr, old_len, new_len, new_addr, locked);
446         if (!(ret & ~PAGE_MASK))
447                 goto out;
448 out1:
449         vm_unacct_memory(charged);
450 
451 out:
452         return ret;
453 }
454 
455 static int vma_expandable(struct vm_area_struct *vma, unsigned long delta)
456 {
457         unsigned long end = vma->vm_end + delta;
458         if (end < vma->vm_end) /* overflow */
459                 return 0;
460         if (vma->vm_next && vma->vm_next->vm_start < end) /* intersection */
461                 return 0;
462         if (get_unmapped_area(NULL, vma->vm_start, end - vma->vm_start,
463                               0, MAP_FIXED) & ~PAGE_MASK)
464                 return 0;
465         return 1;
466 }
467 
468 /*
469  * Expand (or shrink) an existing mapping, potentially moving it at the
470  * same time (controlled by the MREMAP_MAYMOVE flag and available VM space)
471  *
472  * MREMAP_FIXED option added 5-Dec-1999 by Benjamin LaHaise
473  * This option implies MREMAP_MAYMOVE.
474  */
475 SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len,
476                 unsigned long, new_len, unsigned long, flags,
477                 unsigned long, new_addr)
478 {
479         struct mm_struct *mm = current->mm;
480         struct vm_area_struct *vma;
481         unsigned long ret = -EINVAL;
482         unsigned long charged = 0;
483         bool locked = false;
484 
485         if (flags & ~(MREMAP_FIXED | MREMAP_MAYMOVE))
486                 return ret;
487 
488         if (flags & MREMAP_FIXED && !(flags & MREMAP_MAYMOVE))
489                 return ret;
490 
491         if (addr & ~PAGE_MASK)
492                 return ret;
493 
494         old_len = PAGE_ALIGN(old_len);
495         new_len = PAGE_ALIGN(new_len);
496 
497         /*
498          * We allow a zero old-len as a special case
499          * for DOS-emu "duplicate shm area" thing. But
500          * a zero new-len is nonsensical.
501          */
502         if (!new_len)
503                 return ret;
504 
505         down_write(&current->mm->mmap_sem);
506 
507         if (flags & MREMAP_FIXED) {
508                 ret = mremap_to(addr, old_len, new_addr, new_len,
509                                 &locked);
510                 goto out;
511         }
512 
513         /*
514          * Always allow a shrinking remap: that just unmaps
515          * the unnecessary pages..
516          * do_munmap does all the needed commit accounting
517          */
518         if (old_len >= new_len) {
519                 ret = do_munmap(mm, addr+new_len, old_len - new_len);
520                 if (ret && old_len != new_len)
521                         goto out;
522                 ret = addr;
523                 goto out;
524         }
525 
526         /*
527          * Ok, we need to grow..
528          */
529         vma = vma_to_resize(addr, old_len, new_len, &charged);
530         if (IS_ERR(vma)) {
531                 ret = PTR_ERR(vma);
532                 goto out;
533         }
534 
535         /* old_len exactly to the end of the area..
536          */
537         if (old_len == vma->vm_end - addr) {
538                 /* can we just expand the current mapping? */
539                 if (vma_expandable(vma, new_len - old_len)) {
540                         int pages = (new_len - old_len) >> PAGE_SHIFT;
541 
542                         if (vma_adjust(vma, vma->vm_start, addr + new_len,
543                                        vma->vm_pgoff, NULL)) {
544                                 ret = -ENOMEM;
545                                 goto out;
546                         }
547 
548                         vm_stat_account(mm, vma->vm_flags, vma->vm_file, pages);
549                         if (vma->vm_flags & VM_LOCKED) {
550                                 mm->locked_vm += pages;
551                                 locked = true;
552                                 new_addr = addr;
553                         }
554                         ret = addr;
555                         goto out;
556                 }
557         }
558 
559         /*
560          * We weren't able to just expand or shrink the area,
561          * we need to create a new one and move it..
562          */
563         ret = -ENOMEM;
564         if (flags & MREMAP_MAYMOVE) {
565                 unsigned long map_flags = 0;
566                 if (vma->vm_flags & VM_MAYSHARE)
567                         map_flags |= MAP_SHARED;
568 
569                 new_addr = get_unmapped_area(vma->vm_file, 0, new_len,
570                                         vma->vm_pgoff +
571                                         ((addr - vma->vm_start) >> PAGE_SHIFT),
572                                         map_flags);
573                 if (new_addr & ~PAGE_MASK) {
574                         ret = new_addr;
575                         goto out;
576                 }
577 
578                 ret = move_vma(vma, addr, old_len, new_len, new_addr, &locked);
579         }
580 out:
581         if (ret & ~PAGE_MASK)
582                 vm_unacct_memory(charged);
583         up_write(&current->mm->mmap_sem);
584         if (locked && new_len > old_len)
585                 mm_populate(new_addr + old_len, new_len - old_len);
586         return ret;
587 }
588 

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